The present invention relates to a rod capable of securely connecting pedicle screws in a pedicle screw system for correcting a damaged or transformed spine and a method and an apparatus for fabricating the same and, more particularly, to a flexible pedicle rod with superelasticity in order to provide flexibility to a fixation between spine segments and a method and an apparatus capable of fabricating the same in mass production.
Generally, when the spine undergoes bad environments of artificial factors and degenerative spine disease and is maintained in abnormal postures for a long time, serious back pain is induced by the press of the nerve system passing through the spinal canal.
In general, in the case where the conservative treatment has an effect on the patients with degenerative spine disease, the patients need the surgical treatment. Particularly, a spinal fusion treatment is carried out in spinal stenosis, spondylolisdthesis and spondylolysis accompanying instability between spinal segments. A conventional surgical treatment to use a rigid rod, which does not have mobility at all, gives rise to many side effects on the patients as time goes on. Therefore, a pedicle fixing apparatus is to be inserted into an injured or wrenched site of the spine in order that the injured or wrenched site is neither suppressed nor is ruined or the part thereof is not pressed or pushed down.
As shown in FIGS. 1 and 2, a conventional pedicle fixing apparatus includes a plurality of pedicle screws 200 which are respectively inserted, as a supporting member, through the pedicle into injured or deformed vertebra, wherein each of the pedicle screws 200 has a head 201 with a U-shaped rod passage 201a; rods 250 for making a correction of the pedicle through an interconnection between the pedicle screws 200; set screws 300 to be inserted into the rod passage 201a for fixing the rods 250; and a transverse link 400 for holding a pair of the rods 250.
In the pedicle fixing apparatus of FIG. 1, the rod plays an important role in the fixation of the deformed vertebra. Therefore, the quality of the material, elasticity, and so on, of the rod has a significant influence on the human body.
Since most conventional rods are formed out of a titanium material for a medical treatment, the rods themselves do not have elasticity. There is a problem in that it is difficult to maintain a normal waist curve because the fusion of the spine segments is conducted according to the shape of the rod after the surgical spine correction. Moreover, after the spine completely fuses to the arrangement form of the rod, since a load is concentrated on the upper segment or the lower segment of the spine into which the pedicle screws are inserted, instability and another stenosis can be caused after several years.
To solve the demerit of the rigid rod, various methods to partially provide elasticity to a part of the rod have been introduced. Particularly, in order to solve the demerit of the conventional rods effectively and to make the surgical correction of spinal deformity easy, the applicant of the present invention introduced a rod for the pedicle fixation using a shape memory alloy such as a Ni—Ti alloy (Nitinol) which is harmless in the human body with high congeniality and has the property similar to the human tissue in superelasticity and absorption nature. For example, the various rods have been introduced in Korean patent application Nos. 2004-76105, 2004-76106, 2004-97833 and 2004-97834.
As shown in FIGS. 3a and 3b, a rod (600) described in the cited references has a body 602 and an elastic member 604, which has a coil type formed in the middle of the body 602, to provide the flexibility to the rod 600. This flexible rod has a length of approximately 80 to 100 mm (typically, 82 mm) and a small standard diameter of approximately 3 to 6 mm. Since the material of the rod itself is to have the hard metal organization and the rod is to be manufactured in a coil type with the shape memory through a heating process, it is very difficult to form the elastic member of the coil type in the middle of the rod. The rod having the coil section is manually made due to the drawback to the manufacture of the rod; however, it is very difficult to make the rod uniform and it is impossible to realize the mass production and commercialization.
On the other hand, when the surgical correction of spinal deformity, in which two parts of the rod body are different from each other in height, is performed, the elastic member having a large volume causes a surgical inconvenience in the procedure of securing the rod within the pedicle screw because the body described in the cited references is positioned at the central axis of the elastic member and then the pedicle can be in contact with the elastic member. In this case, there is a problem in that an inevitable operation procedure which has to dig a space out of the spine is required.